"He is not going to let this whip him, and he's upbeat," President Bush said of his press secretary. "And so my message to Tony is, 'Stay strong; a lot of people love you and care for you and will pray for you.'"
Snow, 51, had his colon removed in 2005 and underwent six months of chemotherapy after being diagnosed with colon cancer. He underwent surgery on Monday to remove a growth in his abdominal area, near the site of the original cancer.
Doctors determined the growth was cancerous and the cancer had metastasized, or spread, to the liver.
The cancer has attached to the liver but is not in the liver, White House deputy press secretary Dana Perino said.
The news rocked the White House. Snow had gone into the surgery saying he felt fine, and recent blood tests and imaging scans had indicated no return of cancer. He had said he opted to remove the growth out of "aggressive sense of caution."
A former radio and TV commentator, Snow brought his star power and camera-ready charm to a beleaguered White House last May. He quickly became the public face of Bush's daily communications and has spoken openly — and emotionally — about being a cancer survivor.
He had recently reached the two-year mark of being free of cancer.
"He told me that he beat this thing before," said Perino, "and he intends to beat it again."
It is common for colon cancer patients to suffer a recurrence of cancer, and the most common site is the liver. Medical experts say advances in chemotherapy can allow people with the type of cancer Snow has to return to work and good health for years.
But experts declined to speculate on Snow specifically because many details of his condition are unknown. Among the unanswered questions are how far the cancer spread, how extensive the cancer affecting his liver is, and whether the cancer can be surgically removed if it hasn't been already.
"This is a very treatable condition," said Dr. Allyson Ocean, a gastrointestinal oncologist at Weill Cornell Medical College. "Many patients, because of the therapies we have, are able to work and live full lives with quality while they're being treated. Anyone who looks at this as a death sentence is wrong."
Researchers are developing an arsenal of weapons against cancer, the most promising of which are targeted drug therapies, reports CBS News medical correspondent Dr. Jon LaPook. Instead of blasting the entire body with chemotherapy or radiation, targeted therapies hone in on the cancer cells while leaving normal cells relatively unharmed.
"For each tumor we believe there is a critical Achilles heel," says Dr. Robert Weinberg, a cancer researcher at MIT's Whitehead Institute for Biomedical Research. "And if we attack the Achilles heel, we can kill the tumor."
Weinberg adds, "The war on cancer is not going to be won with one dramatic victory. It's a lot of small skirmishes, so that cancer in many cases will one day become a chronic and quite bearable disease rather than one that threatens death."
Perino said Snow is feeling fine after his surgery and has pledged to fight the disease aggressively, likely with chemotherapy but perhaps with other treatments as well. He will be in the hospital recovering from the surgery, a major procedure, for about a week.
Perino broke into tears as she spoke to reporters Tuesday morning. She said Snow also gave her some instructions to pass on to reporters: "Tell them not to bug me." Throughout the day, lawmakers and members of the public sent good wishes to the White House.
Among them was Sen. John Edwards, a presidential candidate whose wife, Elizabeth, learned last week that her breast cancer had returned in an incurable but treatable form. Snow had publicly lauded her that day for dealing with her cancer without fear. At the time of those comments, Snow knew he was about to undergo more surgery of his own, although he did not know what the tests would show.
"Tony has been an incredible example for people living with cancer and cancer survivors," John Edwards said Tuesday.
Some 153,760 Americans will be diagnosed with colorectal cancer this year, and more than 52,000 will die of the disease.
Chemotherapy is a mainstay when the cancer has spread to more than one site, with the hope of controlling, even shrinking, tumors to prolong life.
Snow sent word that he intends to return to the White House and that his job is still very much on his mind, reports CBS News senior White House correspondent Bill Plante. His deputy says he's still focused on the president's battles with Congress and that he gave his staff marching orders for the day.
Perino is leading the news briefings in his absence, which had been expected to be several weeks even before the discovery that his cancer had come back.
Snow and his wife, Jill, have three children, 10, 11 and 14.
"Tony Snow loves this job," Perino said. "He says it is the best job he's ever had in his life. He, in fact, has called it 'Communications Disneyland.' And I think his intention, of course, is to come back. The president wants to have him back."